Positive electrode for lithium primary cell and its production method, and lithium primary cell

ABSTRACT

In a lithium primary cell comprising a positive electrode, a negative electrode and an electrolyte containing an aprotic organic solvent and a support salt, the discharge capacity and energy density of the cell are improved and the service life is prolonged by applying a paste body containing an active substance for positive electrode and a phosphazene derivative and/or an isomer of a phosphazene derivative to the positive electrode.

TECHNICAL FIELD

This invention relates to a positive electrode for a lithium primarycell and a method of producing the same, and a lithium primary cellprovided with such a positive electrode.

BACKGROUND ART

Recently, cells having a small size, a light weight, a long life and ahigh energy density are particularly demanded with the rapid advance ofelectronics as a power source for small-size electronic equipments. Inthis connection, lithium primary cells using, for example, manganesedioxide or graphite fluoride as a positive electrode and lithium as anegative electrode are known as one of cells having a high energydensity because an electrode potential of lithium is lowest among metalsand an electric capacity per unit volume is large, and many kindsthereof are actively studies.

On the other hand, there are developed run-flat tires capable ofcontinuously running up to a repairing service place over a significantdistance even if puncture or the like is caused in a pneumatic tire.Based on this, it is proposed to arrange on the run-flat tire aninternal pressure alarm device which measures a tire internal pressureand transmits an accident-informing signal when the internal pressure isdropped to not more than a constant value.

As a power source for the internal pressure alarm device is used theabove lithium primary cell having a small size, a light weight, a longlife and a high energy density and using manganese dioxide or graphitefluoride as a positive electrode and lithium as a negative electrode.

In the lithium primary cell, lithium is frequently used as a materialforming the negative electrode. However, since lithium violently reactswith a compound having an active proton such as water or alcohol, anelectrolyte to be used is limited to a non-aqueous or solid electrolyte.Since the solid electrolyte is low in the ion conductivity, it islimited only to the use at a low discharge current. Therefore, theelectrolyte usually used at the present time is an aprotic organicsolvent such as ester based organic solvent or the like.

DISCLOSURE OF THE INVENTION

However, it is demanded to upgrade the function of the internal pressurealarm device so as to transmit various informations of the tire inaddition to the tire internal pressure, and a power consumption isincreased accompanied therewith, so that there are caused problems thatthe service life becomes short and the exchange is required in a shorttime when the existing lithium primary cell is used in the power sourcefor such an internal pressure alarm device.

Also, the material for the negative electrode is a lithium metal or alithium alloy and is very high in the activity to water, so that thereis a problem that when the sealing of the cell is incomplete and wateris penetrated into the cell, the negative electrode material reacts withwater to produce hydrogen or cause ignition and hence the risk becomeshigh. Furthermore, since the lithium metal is low in the boiling point(about 170° C.), as a large current rapidly flows in theshort-circuiting or the like, there is a problem that the cellabnormally generates heat to cause a very risky state such as the fusionof the cell or the like. In addition, there is a problem that theelectrolyte based on the organic solvent is vaporized and decomposedaccompanied with the above heat generation of the cell to produce a gasor the explosion-ignition of the cell is caused by the produced gas orthe like. Moreover, even in the lithium primary cell not naturallyassuming the recharge, there is a problem that the recharge may becarried out by wrong operation and in this case the ignition is caused.

It is, therefore, an object of the invention to provide a lithiumprimary cell having a high discharge capacity, a high energy density, ahigh output and a long service life. It is another object of theinvention to provide a lithium primary cell having a high safety inaddition to the high discharge capacity, high energy density, highoutput and long service life.

The inventors have made various studies in order to solve theaforementioned problems and found that lithium primary cells having ahigh discharge capacity, a high energy density, a high output and a longservice life are obtained by improving an active substance for positiveelectrode in the lithium primary cell to lower an internal resistance ofthe cell itself, and further lithium primary cells having a high safetyin addition to higher discharge capacity and energy density, high outputand long service life are obtained by adding a phosphazene derivativeand/or an isomer of a phosphazene derivative to an electrolyte, and as aresult, the invention has been accomplished.

That is, the invention is as follows.

1. A positive electrode for a lithium primary cell comprising a pastebody containing an active substance for positive electrode and aphosphazene derivative and/or an isomer of a phosphazene derivative.

2. A positive electrode for a lithium primary cell according to the item1, wherein a total mass of the phosphazene derivative and/or the isomerof the phosphazene derivative is a mass corresponding to 0.01 to 100times a mass of the active substance for positive electrode.

3. A positive electrode for a lithium primary cell according to the item1 or 2, wherein the phosphazene derivative has a viscosity at 25° C. ofnot more than 100 mPa·s (100 cP) and is represented by the followingformula (I) or (II):

(wherein R¹, R² and R³ are independently a monovalent substituent or ahalogen element; X¹ is a substituent containing at least one elementselected from the group consisting of carbon, silicon, germanium, tin,nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur,selenium, tellurium and polonium; and Y¹, Y² and Y³ are independently abivalent connecting group, a bivalent element or a single bond)(NPR⁴ ₂)_(n)  (II)(wherein R⁴ is independently a monovalent substituent or a halogenelement; and n is 3 to 15).

4. A positive electrode for a lithium primary cell according to the item3, wherein the phosphazene derivative of the formula (II) is representedby the following formula (III):(NPF₂)_(n)  (III)(wherein n is 3 to 15).

5. A positive electrode for a lithium primary cell according to the item3, wherein the phosphazene derivative of the formula (II) is representedby the following formula (IV):(NPR⁵ ₂)_(n)  (IV)(wherein R⁵ is independently a monovalent substituent or a halogenelement and at least one of all R⁵s is a fluorine-containing monovalentsubstituent or fluorine, and n is 3 to 15, provided that all R⁵s are notfluorine).

6. A positive electrode for a lithium primary cell according to the item1 or 2, wherein the phosphazene derivative is a solid at 25° C. and isrepresented by the following formula (V):(NPR⁶ ₂)_(n)  (V)(wherein R⁶ is independently a monovalent substituent or a halogenelement; and n is 3 to 15).

7. A positive electrode for a lithium primary cell according to the item1 or 2, wherein the isomer is represented by the following formula (VI)and is an isomer of a phosphazene derivative represented by thefollowing formula (VII):

(in the formulae (VI) and (VII), R⁷, R⁸ and R⁹ are independently amonovalent substituent or a halogen element; X² is a substituentcontaining at least one element selected from the group consisting ofcarbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic,antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium; andY⁷ and Y⁸ are independently a bivalent connecting group, a bivalentelement or a single bond).

8. A method of producing a positive electrode for a lithium primarycell, characterized by comprising (I) a step of milling an activesubstance for positive electrode and a phosphazene derivative and/or anisomer of a phosphazene derivative to produce a paste; and (II) a stepof applying the paste to a positive electrode manufacturing jig anddrying and shaping into a desired form to produce a positive electrodeof a paste body.

9. A lithium primary electrode comprising a positive electrode describedin any one of the items 1 to 7, a negative electrode, and an electrolytecomprising an aprotic organic solvent and a support salt.

10. A lithium primary cell according to the item 9, wherein the aproticorganic solvent is added with a phosphazene derivative and/or an isomerof a phosphazene derivative.

11. A lithium primary cell according to the item 10, wherein thephosphazene derivative and/or the isomer of the phosphazene derivativeincluded in the positive electrode are the same as the phosphazenederivative and/or the isomer of the phosphazene derivative added to theaprotic organic solvent.

12. A lithium primary cell according to the item 10, wherein thephosphazene derivative and/or the isomer of the phosphazene derivativeincluded in the positive electrode are different from the phosphazenederivative and/or the isomer of the phosphazene derivative added to theaprotic organic solvent.

13. A lithium primary cell according to any one of the items 10 to 12,wherein the phosphazene derivative added to the aprotic organic solventhas a viscosity at 25° C. of not more than 100 mPa·s (100 cP) and isrepresented by the following formula (I) or (II):

(wherein R¹, R² and R³ are independently a monovalent substituent or ahalogen element; X¹ is a substituent containing at least one elementselected from the group consisting of carbon, silicon, germanium, tin,nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur,selenium, tellurium and polonium; and Y¹, Y² and Y³ are independently abivalent connecting group, a bivalent element or a single bond)(NPR⁴ ₂)_(n)  (II)(wherein R⁴ is independently a monovalent substituent or a halogenelement; and n is 3 to 15).

14. A lithium primary cell according to the item 13, wherein thephosphazene derivative of the formula (II) is represented by thefollowing formula (III):(NPF₂)_(n)  (III)(wherein n is 3 to 15).

15. A lithium primary cell according to the item 13, wherein thephosphazene derivative of the formula (II) is represented by thefollowing formula (IV):(NPR⁵ ₂)_(n)  (IV)(wherein R⁵ is independently a monovalent substituent or a halogenelement and at least one of all R⁵s is a fluorine-containing monovalentsubstituent or fluorine, and n is 3 to 15, provided that all R⁵s are notfluorine).

16. A lithium primary cell according to any one of the items 10 to 12,wherein the phosphazene derivative added to the aprotic organic solventis a solid at 25° C. and is represented by the following formula (V):(NPR⁶ ₂)_(n)  (V)(wherein R⁶ is independently a monovalent substituent or a halogenelement; and n is 3 to 15).

17. A lithium primary cell according to any one of the items 10 to 12,wherein the isomer of the phosphazene derivative added to the aproticorganic solvent is represented by the following formula (VI) and is anisomer of a phosphazene derivative represented by the following formula(VII):

(in the formulae (VI) and (VII), R⁷, R⁸ and R⁹ are independently amonovalent substituent or a halogen element; X is a substituentcontaining at least one element selected from the group consisting ofcarbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic,antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium; andY⁷ and Y⁸ are independently a bivalent connecting group, a bivalentelement or a single bond).

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in detail below. In general, a sum ofresistance of each material constituting the cell, and resistanceproduced at each interface between the materials such as betweenelectrolyte and positive electrode, between electrolyte and negativeelectrode or the like corresponds to an internal resistance of the cellitself. As the internal resistance becomes large, the drop of dischargepotential of the cell called as IR drop, which is represented by productof resistance and current applied, is caused. The drop of dischargepotential brings about the shortening of a time required in thedescending up to a constant voltage (i.e. service life of the cell), andhence admits to drops of the discharge capacity and energy density.

The existing lithium primary cell using manganese dioxide or graphitefluoride as an active substance for a positive electrode can not copewith the increase of the power consumption accompanied with theenhancement of the function of the device using such a lithium primarycell as previously mentioned, so that it is required to develop lithiumprimary cells having higher discharge capacity and energy density,higher output and longer service life. For this end, the inventors haveaimed at the active substance for positive electrode and the internalresistance of the cell itself produced inside the cell and made variousstudies, and found out that the positive electrode comprising a pastebody containing an active substance for positive electrode and aphosphazene derivative and/or an isomer of a phosphazene derivative canmake the internal resistance of the cell itself small and hence thedischarge capacity and energy density can be improved to provide alithium primary cell having a high output and a long service life. Also,it has been found out that the internal resistance of the cell itselfcan be made further small by using the positive electrode comprising apaste body containing an active substance for positive electrode and aphosphazene derivative and/or an isomer of a phosphazene derivative andan electrolyte containing a phosphazene derivative and/or an isomer of aphosphazene derivative and hence the discharge capacity and energydensity can be considerably improved to provide a lithium primary cellhaving a considerably higher output and a longer service life.

<Positive Electrode for Lithium Primary Cell>

The positive electrode of the paste body according to the invention is ashaped body of semi-solid mixture formed by locking the phosphazenederivative and/or the isomer of the phosphazene derivative betweenparticles of the active substance for positive electrode, in which thephosphazene derivative and/or the isomer of the phosphazene derivativenever exudes on the surface of the shaped body even if a given force isapplied. The positive electrode of the invention contains additivesusually used in the technical field of the lithium primary cell such asan electrically conductive material, a binding agent and the like, ifnecessary.

Active Substance for Positive Electrode

The active substance for positive electrode used in the invention is asubstance directly contributing to an electromotive reaction at thepositive electrode of the cell and is not particularly limited and canbe used by properly selecting from well-known active substances. Forexample, there are preferably mentioned graphite fluoride((CF_(x))_(n)), MnO₂ (which may be produced by electrochemical synthesisor chemical synthesis), V₂O₅, MoO₃, Ag₂CrO₄, CuO, CuS, FeS₂, SO₂, SOC1₂,TiS₂ and so on. Among them, MnO₂, V₂O₅ and graphite fluoride arepreferable in a point that the capacity, safety and discharge potentialare high and the wettability to the electrolyte is excellent, and MnO₂and V₂O₅ are more preferable in view of the cost. These substances maybe used alone or in a combination of two or more.

The active substance for positive electrode has a particle size of 1-60μm, preferably 20-40 μm. When the particle size is less than 1 μm orexceeds 60 μm, the packing is deteriorated in the shaping of a positiveelectrode combined member (consisting of the active substance forpositive electrode, electrically conductive material and binding agent)or the amount of the active substance for positive electrode containedper unit volume becomes less and hence the discharge capacity isunfavorably decreased.

Phosphazene Derivative and/or Isomer of Phosphazene Derivative

A total mass of a phosphazene derivative and/or an isomer of aphosphazene derivative in the positive electrode of the invention ispreferably 0.01-100 times, more preferably 0.05-50 times, furtherpreferably 0.1-30 times a mass of the active substance for positiveelectrode. When the total mass of the phosphazene derivative and/or theisomer of the phosphazene derivative is less than 0.01 times the mass ofthe active substance for positive electrode, the effect of lowering theinternal resistance of the cell itself by incorporating the phosphazenederivative and/or the isomer of the phosphazene derivative into thepositive electrode together with the active substance for positiveelectrode is insufficient, while when it exceeds 100 times, the amountof the active substance for positive electrode per unit volume isdecreased and also a suspension is unfavorably produced without formingthe paste body.

The phosphazene derivative included in the positive electrode is notparticularly limited, but is preferable to be a phosphazene derivativehaving a viscosity at 25° C. of not more than 100 mPa·s (100 cP) andrepresented by the following formula (I) or (II):

(wherein R¹, R² and R³ are independently a monovalent substituent or ahalogen element; X¹ is a substituent containing at least one elementselected from the group consisting of carbon, silicon, germanium, tin,nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur,selenium, tellurium and polonium; and Y¹, Y² and Y³ are independently abivalent connecting group, a bivalent element or a single bond)(NPR⁴ ₂)_(n)  (II)(wherein R⁴ is independently a monovalent substituent or a halogenelement; and n is 3 to 15).

The viscosity at 25° C. of the phosphazene derivative represented by theformula (I) or (II) is not more than 100 mPa·s (100 cP) as mentionedabove, preferably not more than 20 mPa·s (20 cP).

Moreover, the viscosity in the invention is determined by using aviscosity measuring meter (R-type viscometer Model RE500-SL, made byToki Sangyo Co., Ltd.) and conducting the measurement at each revolutionrate of 1 rpm, 2 rpm, 3 rpm, 5 rpm, 7 rpm, 10 rpm, 20 rpm and 50 rpm for120 seconds to measure a viscosity under the revolution rate when anindication value is 50-60% as an analytical condition.

In the formula (I), R¹, R² and R³ are not particularly limited unlessthey are a monovalent substituent or a halogen element. As themonovalent substituent are mentioned an alkoxy group, an alkyl group, acarboxyl group, an acyl group, an aryl group and so on. Among them, thealkoxy group is preferable. As the halogen element are preferablymentioned fluorine, chlorine, bromine and so on. All of R¹-R³ may be thesame kind of the substituent, or some of them may be different kind ofsubstituents.

As the alkoxy group are mentioned, for example, methoxy group, ethoxygroup, propoxy group, butoxy group and the like, or analkoxy-substituted alkoxy group such as methoxyethoxy group,methoxyethoxyethoxy group or the like. Among them, methoxy group, ethoxygroup, propoxy group, methoxyethoxy group or methoxyethoxyethoxy groupis preferable as all of R¹-R³, and methoxy group, ethoxy group,n-propoxy group or i-propoxy group is particularly preferable. As thealkyl group are mentioned methyl group, ethyl group, propyl group, butylgroup, pentyl group and so on. As the acyl group are mentioned formylgroup, acetyl group, propionyl group, butylyl group, isobutylyl group,valelyl group and so on. As the aryl group are mentioned phenyl group,tolyl group, naphthyl group and so on.

In these monovalent substituents, it is preferable that hydrogen elementis substituted with a halogen element. As the halogen element arepreferably mentioned fluorine, chlorine, bromine and so on.

As the bivalent connecting group shown by Y¹, Y² and Y³ in the formula(I) are mentioned, for example, CH₂ group as well as a bivalentconnecting group containing at least one element selected from the groupconsisting of oxygen, sulfur, selenium, nitrogen, boron, aluminum,scandium, gallium, yttrium, indium, lanthanum, thallium, carbon,silicon, titanium, tin, germanium, lead, phosphorus, vanadium, arsenic,niobium, antimony, tantalum, bismuth, chromium, molybdenum, tellurium,polonium, tungsten, iron, cobalt and nickel. Among them, CH₂ group andthe bivalent connecting group containing at least one element selectedfrom the group consisting of oxygen, sulfur, selenium and nitrogen arepreferable, and the bivalent connecting group containing sulfur and/orselenium is particularly preferable. Also, Y¹, Y² and Y³ are a bivalentelement such as oxygen, sulfur, selenium or the like, or a single bond.All of Y¹-Y³ may be the same kind, or some thereof may be differentkind.

As X¹ in the formula (I) is preferable a substituent containing at leastone element selected from the group consisting of carbon, silicon,nitrogen, phosphorus, oxygen and sulfur from a viewpoint of theharmfulness and the consideration on environment or the like. Amongthese substituents, a substituent having a structure shown by thefollowing formula (VIII), (IX) or (X) is more preferable.

In the formulae (VIII), (IX) and (X), R¹⁰-R¹⁴ are a monovalentsubstituent or a halogen element. Y¹⁰-Y¹⁴ are a bivalent connectinggroup, a bivalent element or a single bond, and Z¹ is a bivalent groupor a bivalent element.

As R¹⁰-R¹⁴ in the formulae (VIII), (IX) and (X) are preferably mentionedthe same monovalent substituents or halogen elements as described onR¹-R³ of the formula (I). Also, they may be the same kind in the samesubstituent, or some of them may be different kind. Further, R¹⁰ and R¹¹of the formula (VIII), and R¹³ and R¹⁴ of the formula (X) may be bondedto each other to form a ring.

As the group shown by Y¹⁰-Y¹⁴ in the formulae (VIII), (IX) and (X) arementioned the same bivalent connecting groups or bivalent elements asdescribed on Y¹-Y³ of the formula (I), and the group containing sulfurand/or selenium is particularly preferable. They may be the same kind inthe same substituent, or some of them may be different kind.

As Z¹ in the formula (III) are mentioned, for example, CH₂ group, CHRgroup (R is an alkyl group, an alkoxy group, a phenyl group or the like,and so forth), NR group as well as a bivalent group containing at leastone element selected from the group consisting of oxygen, sulfur,selenium, boron, aluminum, scandium, gallium, yttrium, indium,lanthanum, thallium, carbon, silicon, titanium, tin, germanium,zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony,tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten,iron, cobalt and nickel. Among them, CH₂ group, CHR group, NR group andthe bivalent group containing at least one element selected from thegroup consisting of oxygen, sulfur and selenium are preferable.Particularly, the bivalent group containing sulfur and/or selenium ispreferable. Also, Z¹ may be a bivalent element such as oxygen, sulfur,selenium or the like.

In the formula (II), R⁴ is not particularly limited unless it is amonovalent substituent or a halogen element. As the monovalentsubstituent are mentioned an alkoxy group, an alkyl group, a carboxylgroup, an acyl group, an aryl group and so on. Among them, the alkoxygroup is preferable. As the halogen element are preferably mentionedfluorine, chlorine, bromine and so on. As the alkoxy group are mentionedmethoxy group, ethoxy group, methoxyethoxy group, propoxy group, phenoxygroup and so on. Among them, methoxy group, ethoxy group, n-propoxygroup and phenoxy group are particularly preferable. In thesesubstituents, hydrogen element is preferable to be substituted with ahalogen element. As the halogen element are preferably mentionedfluorine, chlorine, bromine and so on. As a substituent substituted withfluorine atom is mentioned, for example, trifluoroethoxy group.

The synthesis of phosphazene derivatives having a more preferableviscosity is made possible by properly selecting R¹-R⁴, R¹⁰-R¹⁴, Y¹-Y³,Y¹⁰-Y¹⁴ and Z¹ in the formulae (I), (II), (VIII)-(X). These phosphazenederivatives may be used alone or in a combination of two or more.

Among the phosphazene derivatives of the formula (II), a phosphazenederivative represented by the following formula (III) is particularlypreferable:(NPF₂)_(n)  (III)(wherein n is 3-15).

The phosphazene derivatives of the formula (III) may be used alone or ina combination of two or more.

Among the phosphazene derivatives of the formula (II), a phosphazenederivative represented by the following formula (IV) is particularlypreferable:(NPR⁵ ₂)_(n)  (IV)(wherein R⁵ is independently a monovalent substituent or a halogenelement and at least one of all R⁵s is a fluorine-containing monovalentsubstituent or fluorine, and n is 3-15, provided that all R⁵s are notfluorine).

As the monovalent substituent in the formula (IV) are mentioned analkoxy group an alkyl group, an aryl group, a carboxyl group and so on,and the alkoxy group is particularly preferable. As the alkoxy group arementioned methoxy group, ethoxy group, n-propoxy group, i-propoxy group,butoxy group, an alkoxy group-substituted alkoxy group such asmethoxyethoxy group or the like, and so on, and methoxy group, ethoxygroup and n-propoxy group are particularly preferable.

The monovalent substituent is preferable to be substituted withfluorine. When all R⁵s is in the formula (IV) are not fluorine, at leastone monovalent substituent contains fluorine. The content of fluorine inthe phosphazene derivative is preferably 3-70% by weight, morepreferably 7-45% by weight. As the molecular structure of thephosphazene derivative represented by the formula (IV), a halogenelement such as chlorine, bromine or the like may be contained inaddition to fluorine.

The phosphazene derivatives of the formula (IV) may be used alone or ina combination of two or more.

As the phosphazene derivative included in the positive electrode, aphosphazene derivative being solid at 25° C. and represented by thefollowing formula (V) is preferable:(NPR⁶ ₂)_(n)  (V)(wherein R⁶ is independently a monovalent substituent or ahalogen-element; and n is 3-15).

In the formula (V), R⁶ is not particularly limited unless it is amonovalent substituent or a halogen element. As the monovalentsubstituent are mentioned an alkoxy group, an alkyl group, a carboxylgroup, an acyl group, an aryl group and so on. As the halogen elementare preferably mentioned fluorine, chlorine, bromine and so on. Amongthem, the alkoxy group is particularly preferable.

As the alkoxy group are preferable methoxy group, ethoxy group,methoxyethoxy group, propoxy group (isopropoxy group, n-propoxy group),phenoxy group, trifluoroethoxy group and so on, and methoxy group,ethoxy group, propoxy group (isopropoxy group, n-propoxy group), phenoxygroup, trifluoroethoxy group and so on are more preferable. Themonovalent substituent is preferable to contain the aforementionedhalogen element.

As the phosphazene derivative of the formula (V) are particularlypreferable a structure that R⁶ is methoxy group and n is 3 in theformula (V), a structure that R⁶ is at least either methoxy group orphenoxy group and n is 4 in the formula (V), a structure that R⁶ isethoxy group and n is 4 in the formula (V), a structure that R⁶ isisopropoxy group and n is 3 or 4 in the formula (V), a structure that R⁶is n-propoxy group and n is 4 in the formula (V), a structure that R⁶ istrifluoroethoxy group and n is 3 or 4 in the formula (V), and astructure that R⁶ is phenoxy group and n is 3 or 4 in the formula (V).

The molecular structure of the phosphazene derivative represented by theformula (V) is preferable to have a substituent containing a halogenelement as previously mentioned. As the halogen element are preferablefluorine, chlorine, bromine and so on, and fluorine is particularlypreferable.

The phosphazene derivatives of the formula (V) may be used alone or in acombination of two or more.

The isomer of the phosphazene derivative included in the positiveelectrode is not particularly limited, but is preferable to berepresented by the following formula (VI) and be an isomer of aphosphazene derivative shown by the following formula (VII):

(in the formulae (VI) and (VII), R⁷, R⁸ and R⁹ are independently amonovalent substituent or a halogen element; X² is a substituentcontaining at least one element selected from the group consisting ofcarbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic,antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium; andY⁷ and Y⁸ are independently a bivalent connecting group, a bivalentelement or a single bond).

In the formula (VI), R⁷, R⁸ and R⁹ are not particularly limited unlessthey are a monovalent substituent or a halogen element. As themonovalent substituent are mentioned an alkoxy group, an alkyl group, acarboxyl group, an acyl group, an aryl group and so on. As the halogenelement are preferably mentioned fluorine, chlorine, bromine and so on.Among them, fluorine and alkoxy group are particularly preferable. Also,fluorine, alkoxy group and alkoxy group containing fluorine or the likeare preferable. All of R⁷-R⁹ may be the same kind of the substituent, orsome of them may be different kind of substituents.

As the alkoxy group are mentioned, for example, methoxy group, ethoxygroup, propoxy group, butoxy group and the like, and analkoxy-substituted alkoxy group such as methoxyethoxy group,methoxyethoxyethoxy group or the like. Among them, methoxy group, ethoxygroup, methoxyethoxy group or methoxyethoxyethoxy group is preferable asall of R⁷-R⁹, and methoxy group or ethoxy group is particularlypreferable. As the alkyl group are mentioned methyl group, ethyl group,propyl group, butyl group, pentyl group and so on. As the acyl group arementioned formyl group, acetyl group, propionyl group, butylyl group,isobutylyl group, valelyl group and so on. As the aryl group arementioned phenyl group, tolyl group, naphthyl group and so on.

In these substituents, hydrogen element is preferable to be substitutedwith a halogen element. As the halogen element are preferably mentionedfluorine, chlorine, bromine and so on.

As the bivalent connecting group shown by Y⁷ and Y⁸ in the formula (VI)are mentioned, for example, CH₂ group, and a bivalent connecting groupcontaining at least one element selected from the group consisting ofoxygen, sulfur, selenium, nitrogen, boron, aluminum, scandium, gallium,yttrium, indium, lanthanum, thallium, carbon, silicon, titanium, tin,germanium, zirconium, lead, phosphorus, vanadium, arsenic, niobium,antimony, tantalum, bismuth, chromium, molybdenum, tellurium, polonium,tungsten, iron, cobalt and nickel. Among them, CH₂ group and thebivalent connecting group containing at least one element selected fromthe group consisting of oxygen, sulfur, selenium and nitrogen arepreferable. Also, Y⁷ and Y⁸ may be a bivalent element such as oxygen,sulfur, selenium or the like, or a single bond. The bivalent connectinggroup containing sulfur and/or oxygen, oxygen element, and sulfurelement are more preferable, and the bivalent connecting groupcontaining oxygen and oxygen element are particularly preferable. Y⁷ andY⁸ may be the same kind or different kinds.

In the formula (VI), X² is preferable to be a substituent containing atleast one element selected from the group consisting of carbon, silicon,nitrogen, phosphorus, oxygen and sulfur from a viewpoint of harmfulnessand consideration on environment or the like, and a substituent having astructure shown by the following formula (XI), (XII) or (XIII) is morepreferable:

In the formulae (XI), (XII) and (XIII), R¹⁵-R¹⁹ are a monovalentsubstituent or a halogen element. Y¹⁵-Y¹⁹ are a bivalent connectinggroup, a bivalent element or a single bond, and Z² is a bivalent groupor a bivalent element.

As R¹⁵-R¹⁹ in the formulae (XI), (XII) and (XIII) are preferablymentioned the same monovalent substituents or halogen elements asdescribed in R⁷-R⁹ of the formula (VI). They may be the same kind in thesame substituent, or some of them may be different kinds. R¹⁵ and R¹⁶ inthe formula (XI), and R¹⁸ and R¹⁹ in the formula (XIII) may be bonded toeach other to form a ring.

As the groups shown by Y¹⁵-Y¹⁹ in the formula (XI), (XII) and (XIII) arementioned the same bivalent connecting groups, bivalent elements or thelike as described in Y⁷-Y⁹ of the formula (VI), and the bivalentconnecting group containing sulfur and/or oxygen, oxygen element andsulfur element are more preferable. Particularly, the bivalentconnecting group containing oxygen and oxygen element are preferable.They may be the same kind in the same substituent, or some of them maybe different kinds.

As Z² of the formula (XI) are mentioned, for example, CH₂ group, CHR′group (R′ is an alkyl group, an alkoxyl group, a phenyl group or thelike, and so forth), NR′ group and a bivalent group containing at leastone element selected from the group consisting of oxygen, sulfur,selenium, boron, aluminum, scandium, gallium, yttrium, indium,lanthanum, thallium, carbon, silicon, titanium, tin, germanium,zirconium, lead, phosphorus, vanadium, arsenic, niobium, antimony,tantalum, bismuth, chromium, molybdenum, tellurium, polonium, tungsten,iron, cobalt and nickel. Among them, CH₂ group, CHR′ group, NR′ groupand the bivalent group containing at least one element selected from thegroup consisting of oxygen, sulfur and selenium are preferable. Also, Z²may be a bivalent element such as oxygen, sulfur, selenium or the like.Particularly, the bivalent group containing sulfur and/or selenium,sulfur element and selenium element are preferable. The bivalent groupcontaining oxygen and oxygen element are more preferable.

By properly selecting R⁷-R⁹, R¹⁵-R¹⁹, Y⁷-Y⁸, Y¹⁵-Y¹⁹ and Z² in theformulae (VI) and (XI)-(XIII) is made possible to synthesis an isomer ofa phosphazene derivative having a more preferable viscosity. Thesecompounds may be used alone or in a combination of two or more.

The isomer of the formula (VI) is an isomer of a phosphazene derivativerepresented by the formula (VII), which can be produced by adjusting avacuum degree and/or a temperature in the production of the phosphazenederivative shown, for example, by the formula (VII). The content of theisomer in the electrolyte (volume %) can be measured by the followingmeasuring method.

<<Measuring Method>>

It can be measured by finding a peak area of a sample through a gelpermeation chromatography (GPC) or a high-speed liquid chromatography,comparing the found peak area with a previously found area per mole ofthe isomer to obtain a molar ratio, and further converting into a volumewhile considering a specific gravity.

As R⁷-R⁹, Y⁷-Y⁸ and X² in the formula (VII) are preferably mentioned thesame ones as described on R⁷-R⁹, Y⁷-Y⁸ and X² of the formula (VI).

As molecular structures of the isomer of the formula (VI) and thephosphazene derivative of the formula (VII), it is preferable to have asubstituent containing a halogen element. As the halogen element,fluorine, chlorine, bromine and the like are preferable, and fluorine isparticularly preferable.

Additive for Positive Electrode

Among additives added, if necessary, to the positive electrode for thelithium primary cell according to the invention, acetylene black and thelike are mentioned as an electrically conductive material, andvinylidene polyfluoride (PVDF), polytetrafluoroethylene (PTFE) and thelike are mentioned as a binding agent. These additives can be used inthe same compounding ratio as in the conventional technique.

Form of Positive Electrode

The form of the positive electrode is not particularly limited, and canbe properly selected from the well-known forms as the electrode. Forexample, there are mentioned a sheet, a column, a plate, a spiral formand so on.

<Production Method of Positive Electrode for Lithium Primary Cell>

The production method of the positive electrode for the lithium primarycell according to the invention is not particularly limited. Forexample, the positive electrode can be produced by the following method.

In the production method of the positive electrode for the lithiumprimary cell according to the invention, a paste is prepared by mixingand milling an active substance for positive electrode and a phosphazenederivative and/or an isomer of a phosphazene derivative as a first step.Moreover, the paste may be added with additives usually used in thetechnical field of the lithium primary cell such as electricallyconductive material, binding agent and the like.

In a second step, the paste prepared in the first step is applied to ajig for the manufacture of the positive electrode. As the jig for themanufacture of the positive electrode can be used a jig usually used inthe technical field of the lithium primary cell. For example, a doctorblade or the like is mentioned.

Then, the paste applied to the jig for the manufacture of the positiveelectrode is dried and shaped into a desired form to produce a positiveelectrode. The drying is preferable to be a hot drying at 100-120° C.Also, as the shaping method can be used the conventionally known method.For example, the paste applied to the jig for the manufacture of thepositive electrode and dried can be punched out by a punching machinewith a mold corresponding to an objective form of a positive electrodefor the lithium primary cell.

In the positive electrode obtained by the above method, the phosphazenederivative and/or the isomer of the phosphazene derivative is closedbetween the particles of the active substance for positive electrode, sothat the internal resistance of the cell itself is small as comparedwith the positive electrode consisting of only the active substance forpositive electrode and hence it is a positive electrode for a lithiumprimary cell having high discharge capacity and energy density, a highoutput and a long service life.

<Lithium Primary Cell>

The lithium primary cell of the invention comprises the aforementionedpositive electrode, a negative electrode, and an electrolyte comprisingan aprotic organic solvent and a support salt, and includes membersusually used in the technical filed of the lithium primary cell such asa separator and the like, if necessary.

Negative Electrode

As a material of the negative electrode in the lithium primary cell ofthe invention, a lithium alloy and the like are mentioned in addition toa lithium metal itself. As a metal to be alloyed with lithium arementioned Sn, Pb, Al, Au, Pt, In, Zn, Cd, Ag, Mg and so on. Among them,Al, Zn and Mg are preferable from a viewpoint of a great depositionamount and a toxicity. These materials may be used alone or in acombination of two or more. The form of the negative electrode is notparticularly limited, and can be properly selected from the samewell-known ones as the aforementioned forms of the positive electrode.

Electrolyte

The electrolyte in the lithium primary cell of the invention comprisesan aprotic organic solvent and a support salt. Since the negativeelectrode in the lithium primary cell is made of the lithium or lithiumalloy as mentioned above, it is very high in the reactivity with water,so that the aprotic organic solvent not reacting with water is used as asolvent.

Aprotic Organic Solvent

The aprotic organic solvent is not particularly limited, but includesether compounds, ester compounds and so on from a view point that theviscosity of the electrolyte is controlled to a low value. Concretely,there are mentioned 1,2-dimethoxyethane (DME), tetrahydrofuran, dimethylcarbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate,propylene carbonate (PC), γ-butyrolactone (GBL), γ-valerolactone,methylethyl carbonate, ethylmethyl carbonate and so on.

Among them, cyclic ester compounds such as propylene carbonate,γ-butyrolactone and the like, chain ester compounds such as dimethylcarbonate, methylethyl carbonate and the like, and chain ether compoundssuch as 1,2-dimethoxyethane and the like are preferable. Particularly,the cyclic ester compound is preferable in a point that the dielectricconstant is high and the solubility to a support salt (lithium salt)mentioned later is excellent, and the chain ester compound and ethercompound are preferable in a point that the viscosity is low and hencethe viscosity of the electrolyte is made low. They may be used alone orin a combination of two or more.

Support Salt

As the support salt may be used any salts usually used as an ion sourcefor lithium ion. The ion source for lithium ion is not particularlylimited, but there are preferably mentioned lithium-salts such asLiClO₄, LiBF₄, LiPF₆, LiCF₃SO₃, LiAsF₆, LiC₄F₉SO₃, Li(CF₃SO₂)₂N,Li(C₂F₅SO₂)₂N and so on. They may be used alone or in a combination oftwo or more.

The content of the support salt in the electrolyte is preferably 0.2-1mol, more preferably 0.5-1 mol per IL of a solvent component in theelectrolyte. When the content is less than 0.2 mol, the sufficientelectric conductivity of the electrolyte can not be ensured and hencethe discharge characteristic of the cell may cause trouble. While, whenit exceeds 1 mol, the viscosity of the electrolyte rises and thesufficient mobility of lithium ion can not be ensured, and hence thesufficient electric conductivity of the electrolyte can not be ensuredas mentioned above and the solution resistance rises, and as a result,the pulse discharge and the low-temperature characteristic may causetrouble.

Phosphazene Derivative and/or Isomer of Phosphazene Derivative

The aprotic organic solvent is preferable to be added with a phosphazenederivative and/or an isomer of a phosphazene derivative.

In the invention, the reason why the phosphazene derivative and/or theisomer of the phosphazene derivative is added to the electrolyte is asfollows. That is, the paste body comprising the active substance forpositive electrode and the phosphazene derivative and/or the isomer ofthe phosphazene derivative is used as the positive electrode aspreviously mentioned, while the phosphazene derivative and/or the isomerof the phosphazene derivative is added to the electrolyte, whereby theinternal resistance of the cell itself is lowered and hence thedischarge capacity and energy density of the lithium primary cell can beimproved by the lowering of the internal resistance, and hence there isobtained a lithium primary cell having a high output and a long servicelife.

In the conventional electrolyte based on the aprotic organic solvent forthe lithium primary cell, when a large current violently flows in theshort-circuiting to abnormally generate heat in the cell, it is a highrisk that a gas is generated by vaporization-decomposition or theexplosion-ignition of the cell is caused by the gas and heat generated,and also it is a high risk that sparks produced in the short-circuitingtake fire in the electrolyte to cause the fire-ignition. If thephosphazene derivative and/or the isomer of the phosphazene derivativeis included in the conventional electrolyte, thevaporization-decomposition or the like of the electrolyte at arelatively low temperature of not higher than about 200° C. iscontrolled to reduce the risk of the ignition-explosion, and even if thefire is caused in the interior of the cell by fusion of the negativeelectrode material or the like, the risk of fire catching is low.Furthermore, phosphorus has an action of suppressing the chaindecomposition of the high polymer material constituting the cell, sothat the risk of the fire-ignition is effectively reduced. Moreover, ifthe phosphazene derivative and/or the isomer of the phosphazenederivative is included in the conventional electrolyte, it is possibleto provide a lithium primary cell having excellent low-temperature andhigh-temperature characteristics.

The phosphazene derivative and the isomer of the phosphazene derivativehave a potential window enough to function as a primary cell, and isnever decomposed by discharge. Also, the phosphazene derivative and theisomer of the phosphazene derivative containing a halogen (e.g.fluorine) functions as an agent catching an active radical in a barecase of combustion, while the phosphazene derivative and the isomer ofthe phosphazene derivative containing an organic substituent have aneffect of shielding oxygen because a carbide (char) is produced on theelectrode material and the separator in the combustion. In addition,even if the recharge is accidentally by a user, the phosphazenederivative and the isomer of the phosphazene derivative have an effectof suppressing the formation of dendrite, so that the safety becomeshigher as compared with the system containing no phosphazene derivativeand the isomer thereof.

In the invention, the risk of fire-ignition is evaluated by themeasurement of oxygen index according to JIS K7201. Moreover, the oxygenindex means a value of minimum oxygen concentration represented by avolume percentage required for maintaining combustion of a materialunder given test conditions defined in JIS K7201, in which the lower theoxygen index, the higher the risk of fire-ignition, and the higher theoxygen index, the lower the risk of fire-ignition. In the invention, therisk of fire-ignition is evaluated by a limit oxygen index according tothe above oxygen index.

The electrolyte added with the phosphazene derivative and/or the isomerof the phosphazene derivative is preferable to have a limit oxygen indexof not less than 21 volume %. When the limit oxygen index is less than21 volume %, the effect of suppressing the fire-ignition is notsufficient. Since the oxygen index is 20.2 volume % under an atmosphericcondition, the limit oxygen index of 20.2 volume % means that combustionoccurs in the atmosphere. The inventors have made various studies andfound that the self-extinguishing property is developed at the limitoxygen index of not less than 21% by volume, and the flame retardance isdeveloped at not less than 23% by volume, and the incombustibility isdeveloped at not less than 25% by volume.

Moreover, the terms “self-extinguishing property, flame retardance,incombustibility” used herein are defined in the method according to UL94HB method, wherein when a test piece of 127 mm×12.7 mm is prepared byimpregnating an electrolyte into an incombustible quartz fiber and isignited under atmospheric environment, the self-extinguishing propertyindicates a case that the ignited flame is extinguished in a linebetween 25 mm and 100 mm and an object fallen down from a net is notfired, and the flame retardance indicates a case that the ignited flamedoes not arrive at a line of 25 mm of the apparatus and the objectfallen down from the net is not fired, and the incombustibilityindicates a case that no ignition is observed (combustion length: 0 mm).

In the invention, the phosphazene derivative and/or the isomer of thephosphazene derivative included in the paste body constituting thepositive electrode may be the same as or different from the phosphazenederivative and/or the isomer of the phosphazene derivative added to theaprotic organic solvent constituting the electrolyte.

As the phosphazene derivative added to the aprotic organic solvent, aphosphazene derivative having a viscosity at 25° C. of not more than 100mPa·s (100 cP), preferably not more than 20 mPa·s (20 cP) andrepresented by the formula (I) or (II) is preferable from a viewpointthat the viscosity is low and the support salt is well dissolved. Whenthe viscosity is exceeds mPa·s (100 cP), the dissolution of the supportsalt is difficult and the wettability to the positive electrodematerial, the separator or the like lowers, and also the ionconductivity is considerably lowered due to the increase of the viscousresistance of the electrolyte, and particularly the performances arelacking in the use under a lower temperature condition below thefreezing point.

Although R¹, R² and R³ in the formula (I) are mentioned above, thealkoxy group is preferable in a point that the viscosity of theelectrolyte can be made low. As the alkoxy group are mentioned theaforementioned alkoxy groups. Among them, methoxy group or ethoxy groupis particularly preferable as all of R¹-R³ from a viewpoint of the lowviscosity and high dielectric constant.

Although the groups of Y¹⁰-Y¹⁴ in the formulae (VIII), (IX) and (X) arementioned above, the group containing sulfur and/or selenium isparticularly preferable as the group of Y¹⁰-Y¹⁴ because the risk offire-ignition in the electrolyte is reduced.

Although Z¹ in the formula (VIII) is mentioned above, the bivalent groupcontaining sulfur and/or selenium is particularly preferable as Z¹because the risk of fire-ignition in the electrolyte is reduced.

Among the substituents in the formulae (VIII)-(X), the substituentcontaining phosphorus as shown by the formula (VIII) is particularlypreferable in a point that the risk of fire-ignition can be reducedeffectively. Also, the substituent containing sulfur as shown by theformula (IX) is particularly preferable in a point that the internalresistance of the cell itself can be reduced.

Although R⁴ in the formula (II) is mentioned above, the alkoxy group ispreferable in a point that the viscosity of the electrolyte can be madelow.

By properly selecting R¹-R⁴, R¹⁰-R¹⁴, Y¹-Y³, Y¹⁰-Y¹⁴ and Z¹ in theformulae (I), (II) and (VIII)-(X), it is made possible to synthesize aphosphazene derivative having a more preferable viscosity and asolubility suitable for addition and mixing as the phosphazenederivative to be added to the aprotic organic solvent.

Among the phosphazene derivatives represented by the formula (II), aphosphazene derivative represented by the formula (III) is particularlypreferable as the phosphazene derivative to be added to the aproticorganic solvent from a viewpoint that the viscosity of the electrolyteis made low to improve the low-temperature characteristic of the celland further improve the deterioration resistance and safety of theelectrolyte.

The phosphazene derivative of the formula (III) is a liquid of a lowviscosity at room temperature (25° C.) and has an action of dropping thesolidifying point. For this end, by adding such a phosphazene derivativeto the electrolyte, it is possible to give an excellent low-temperaturecharacteristic to the electrolyte, and also it is possible to attain thelow viscosity of the electrolyte to provide a lithium primary cellhaving a low internal resistance and a high electric conductivity.Therefore, it is possible to provide a lithium primary cell developingan excellent discharge characteristic over a long period even in the useunder low temperature conditions at low-temperature area or season.

In the formula (III), n is preferable to be 3-4, particularly 3 in apoint that the excellent low-temperature characteristic can be given tothe electrolyte and the viscosity of the electrolyte can be made low.When the value of n is small, the boiling point is low and theignition-preventing property in the approaching to flame can beimproved. On the other hand, as the value of n becomes large, theboiling point becomes high and it can be stably used even at a hightemperature. In order to obtain target performances by utilizing theabove nature, it is possible to properly select and use pluralphosphazene derivatives.

By properly selecting the value of n in the formula (III) can beprepared an electrolyte having a more preferable viscosity, a solubilitysuitable for mixing, a low-temperature characteristic and the like. suchphosphazene derivatives may be used alone or in a combination of two ormore.

The viscosity of the phosphazene derivative of the formula (III) addedto the aprotic organic solvent is not particularly limited unless it isnot more than 20 mPa·s (20 cP), but is preferably not more than 10 mPa·s(10 cP), more preferably not more than 5 mPa·s (5 cP) from a viewpointof the improvement of the electrical conduction and the improvement ofthe low-temperature characteristic.

Among the phosphazene derivatives of the formula (II), a phosphazenederivative represented by the formula (IV) is particularly preferable asthe phosphazene derivative to be added to the aprotic organic solventfrom a viewpoint of the improvements of the deterioration resistance andsafety of the electrolyte.

In case of including the phosphazene derivative of the formula (II), thesafety of the electrolyte can be improved, but it is possible to give amore excellent safety to the electrolyte by including a phosphazenederivative in which at least one of all R⁵s is in the formula (IV) is amonovalent substituent containing fluorine. Furthermore, it is possibleto provide a further excellent safety by including a phosphazenederivative in which at least one of all R⁵s is in the formula (IV) isfluorine. That is, the phosphazene derivative in which at least one ofall R⁵s is in the formula (IV) is a fluorine-containing monovalentsubstituent or fluorine has an effect of hardly burning the electrolyteas compared with the phosphazene derivative containing no fluorine andcan give the more excellent safety to the electrolyte.

Although R⁵ in the formula (IV) is mentioned above, the alkoxy group ispreferable in a point that the improvement of the safety in theelectrolyte is excellent. As the alkoxy group are mentionedaforementioned alkoxy groups, and among them methoxy group, ethoxy groupand n-propoxy group are particularly preferable in view that theimprovement of the safety in the electrolyte is excellent. Also, methoxygroup is preferable in a point that the viscosity of the electrolyte ismade low.

In the formula (IV), n is preferable to be 3-4 in a point that theexcellent safety can be given to the electrolyte.

Although the content of fluorine in the phosphazene derivative of theformula (IV) has been previously mentioned, when the content is withinthe aforementioned range, the effect inherent to the invention of“excellent safety” can be developed preferably.

By properly selecting R⁵ and n in the formula: (IV), it is possible toprepare an electrolyte having more preferable safety and viscosity, asolubility suitable for mixing and the like. Such phosphazenederivatives may be used alone or in a combination of two or more.

The viscosity of the phosphazene derivative of the formula (IV) is notparticularly limited unless it is not more than 20 mPa·s (20 cP), but ispreferably not more than 10 mPa·s (10 cP), more preferably not more than5 mPa·s (5 cP) from a viewpoint of the improvement of the electricalconduction and the improvement of the low-temperature characteristic.

As the phosphazene derivative to be added to the aprotic organicsolvent, a phosphazene derivative of the formula (V) is preferable to bea solid at room temperature (25° C.) from a viewpoint that thedeterioration resistance of the electrolyte is improved whilesuppressing the rise of the viscosity of the electrolyte to thereby givethe self-extinguishing property or flame retardance to the electrolyte.

Since the phosphazene derivative of the formula (V) is a solid at roomtemperature (25° C.), when it is added to the electrolyte, it isdissolved in the electrolyte to raise the viscosity of the electrolyte.However, in case of the given addition amount as mentioned later, therising rate of the viscosity of the electrolyte is low and a lithiumprimary cell having a low internal resistance and a high electricconductivity is provided. In addition, since the phosphazene derivativeof the formula (V) is dissolved in the electrolyte, the stability of theelectrolyte is excellent over a long period. On the other hand, when itis added in an amount exceeding the given value, the viscosity of theelectrolyte becomes considerably large, and the internal resistance ishigh and the electric conductivity is low, and hence the use as thelithium primary cell becomes impossible.

As to R⁶ of the formula (V), there are ones as mentioned above, but thealkoxy group is preferable in a point that the rise of the viscosity ofthe electrolyte can be suppressed. As the alkoxy group are mentioned theaforementioned alkoxy groups. Among them, methoxy group, ethoxy group,propoxy group (isopropoxy group, n-propoxy group), phenoxy group andtrifluoroethoxy group are more preferable in a point that the rise ofthe viscosity of the electrolyte can be suppressed.

In the formula (V), n is particularly preferable to be 3 or 4 in a pointthat the rise of the viscosity of the electrolyte can be suppressed.

As the phosphazene derivative of the formula (V), a structure of theformula (V) that R⁶ is methoxy group and n is 3, a structure of theformula (V) that R⁶ is at least either methoxy group or phenoxy groupand n is 4, a structure of the formula (V) that R⁶ is ethoxy group and nis 4, a structure of the formula (V) that R⁶ is isopropoxy group and nis 3 or 4, a structure of the formula (V) that R⁶ is n-propoxy group andn is 4, a structure of the formula (V) that R⁶ is trifluoroethoxy groupand n is 3 or 4, and a structure of the formula (V) that R⁶ is phenoxygroup and n is 3 or 4 are particularly preferable as the phosphazenederivative to be added to the aprotic organic solvent in a point thatthe rise of the viscosity of the electrolyte can be suppressed.

By properly selecting each substituent and value of n in the formula(V), it is possible to prepare an electrolyte having a more preferableviscosity, a solubility suitable for mixing and the like. Suchphosphazene derivatives may be used alone or in a combination of two ormore.

The isomer of the phosphazene derivative to be added to the aproticorganic solvent is not particularly limited, but an isomer representedby the formula (VI) and of a phosphazene derivative of the formula (VII)is preferable from a viewpoint that the low-temperature characteristicof the lithium primary cell is considerably improved to give aself-extinguishing property or flame retardance to the electrolyte andfurther improve the deterioration resistance of the electrolyte.

Although R⁷, R⁸ and R⁹ in the formula (VI) are mentioned above, fluorineand alkoxy group are particularly preferable in view of thelow-temperature characteristic and the electrochemical stability of theelectrolyte. Also, fluorine, alkoxy group and fluorine-containing alkoxygroup are preferable in a point that the viscosity of the electrolyte ismade low. As the alkoxy group are mentioned the aforementioned alkoxygroups. Among them, all of R⁷-R⁹ are particularly preferable to bemethoxy group or ethoxy group from a viewpoint of low viscosity and highdielectric constant.

Although Y⁷ and Y⁸ in the formula (VI) are mentioned above, the bivalentconnecting group containing sulfur and/or oxygen, oxygen element andsulfur element are particularly preferable in a point that the flameretardance of the electrolyte is improved, and the oxygen-containingbivalent connecting group and oxygen element are particularly preferablein a point that the low-temperature characteristic of the electrolyte isexcellent.

Although Y¹⁵-Y¹⁹ in the formulae (XI), (XII) and (XIII) are mentionedabove, it is particularly preferable that the groups of Y¹⁵-Y¹⁹ are thebivalent connecting group containing sulfur and/or oxygen, oxygenelement or sulfur element because the flame retardance of theelectrolyte is improved. Also, the oxygen-containing bivalent connectinggroup and oxygen element are preferable in a point that thelow-temperature characteristic of the electrolyte is excellent.

Although Z² in the formula (XI) is mentioned above, it is particularlypreferable that Z² is a bivalent group containing sulfur and/orselenium, sulfur element or selenium element because the flameretardance of the electrolyte is improved. Also, the oxygen-containingbivalent group and oxygen element are particularly preferable in a pointthat the low-temperature characteristic of the electrolyte is excellent.

Among the substituents shown by the formulae (XI)-(XIII), aphosphorus-containing substituent as shown by the formula (XI) isparticularly preferable in a point that the self-extinguishing propertyto the flame retardance can be developed effectively. Also, asulfur-containing substituent as shown by the formula (XII) isparticularly preferable in a point that the interfacial resistance ofthe electrolyte is made small.

By properly selecting R⁷-R⁹, R¹⁵-R¹⁹, Y⁷-Y⁸, Y¹⁵-Y¹⁹ and Z² in theformulae (VI) and (XI)-(XIII), it is possible to prepare an electrolytehaving a more preferable viscosity, a solubility for addition andmixing, a low-temperature characteristic and the like. Such compoundsmay be used alone or in a combination of two or more.

Although the phosphazene derivative of the formula (VII) is mentionedabove, ones having a relatively low viscosity and capable of welldissolving the support salt are preferable as the phosphazene derivativeto be added to the aprotic organic solvent.

As the phosphazene derivative of the formula (I), (II), (V) or (VII) orthe isomer of the formula (VI), ones having a halogen-containingsubstituent in their molecular structure are preferable for adding tothe aprotic organic solvent. When the halogen-containing substituent isexistent in the molecular structure, even if the content of thephosphazene derivative or the isomer is small, it is possible toeffectively reduce the risk of fire-ignition in the electrolyte by ahalogen gas derived. Moreover, the occurrence of halogen radical comesinto problem in the compound having a halogen-containing substituent,but the phosphazene derivative or the isomer of the phosphazenederivative used in the invention does not cause such a problem becausephosphorus element in the molecular structure catches the halogenradical to form a stable phosphorus halide.

The content of the halogen element in the phosphazene derivative and theisomer of the phosphazene derivative is preferably 2-80% by weight, morepreferably 2-60% by weight, further preferably 2-50% by weight. When thecontent is less than 2% by weight, the effect by the inclusion of thehalogen element may not be sufficiently developed, while when it exceeds80% by weight, the viscosity becomes higher and the electricconductivity may lower in the addition to the electrolyte. As thehalogen element, fluorine, chlorine, bromine and the like arepreferable, and fluorine is particularly preferable from a viewpoint ofthe provision of good cell characteristics.

A flash point of the phosphazene derivatives represented by the formulae(I), (II), (IV), (V) and (VII) is not particularly limited, but it ispreferably not lower than 100° C., more preferably not lower than 150°C., further preferably not lower than 300° C. from a viewpoint of thefire control and the like. On the other hand, the phosphazene derivativeof the formula (III) has no flash point. The term “flash point” usedherein concretely means a temperature that the flame is widened on asurface of a mass to cover at least 75% of the mass surface. The flashpoint is a measure observing a tendency of forming a combustible mixturewith air. As the phosphazene derivative has a flash point above 100° C.or has not a flash point, the fire or the like is suppressed, and alsoeven if the fire or the like is caused in the interior of the cell, itis possible to lower the risk that it is ignited to outblaze on thesurface of the electrolyte.

By adding the phosphazene derivative of the formula (III) or (V) or theisomer of the formula (VI) and the phosphazene derivative of the formula(VII), the decomposition of the support salt is suppressed toconsiderably stabilize the electrolyte. In the electrolyte comprisingthe ester based organic solvent, which is used in the conventionallithium primary cell, and the support salt as a lithium ion source, thesupport salt is decomposed with the lapse of time and the resultingdecomposed product reacts with a slight amount of water existing in theorganic solvent or the like and hence there may be caused a case oflowering the electrical conductivity of the electrolyte or deterioratingthe electrode material. In this case, LiCF₃SO₃, Li(C₂F₅SO₂)₂N,Li(CF₃SO₂)₂N, which have a low hydrolysis of the support salt itself,are particularly preferable though LiBF₄, LiPF₆, LiCF₃SO₃,Li(C₂F₅SO₂)₂N, Li(CF₃SO₂)₂N and the like are usually used as a supportsalt. However, LiBF₄ and LiPF₆ mat be preferably used owing to the aboveaction.

The contents of the phosphazene derivative and the isomer of thephosphazene derivative in the electrolyte are described below.

From a viewpoint of “limit oxygen index”, the content of the phosphazenederivative of the formula (I) or (II) to the electrolyte is preferablynot less than 5% by volume, more preferably not less than 10% by volume.By adjusting the content to the value of the above range is effectivelyreduced the risk of fire-ignition of the electrolyte. Moreover, theabove range effectively reduces the risk of ignition but differs inaccordance with the kind of the support salt and the kind of electrolyteused, so that it is optimized by properly determining the content sothat the system is controlled to a lowest viscosity and the limit oxygenindex is rendered into not less than 21 volume %.

From a viewpoint of “safety”, the content of the phosphazene derivativeof the formula (III) in the electrolyte is preferably not less than 5%by volume, and the content of the phosphazene derivative of the formula(IV) is preferably not less than 10% by volume, more preferably not lessthan 15% by volume. When the content is within the above range, thesafety of the electrolyte can be preferably improved.

From a viewpoint of “self-extinguishing property”, the content of thephosphazene derivative of the formula (V) is preferably not less than20% by weight, and the total content of the isomer of the formula (VI)and the phosphazene derivative of the formula (VII) is preferably notless than 20% by volume. When the content is within the above range, thesufficient self-extinguishing property can be developed in theelectrolyte.

From a viewpoint of “flame retardance”, the content of the phosphazenederivative of the formula (V) is preferably not less than 30% by weight,and the total content of the isomer of the formula (VI) and thephosphazene derivative of the formula (VII) is preferably not less than30% by volume. When the content is within the above range, thesufficient flame retardance can be developed in the electrolyte.

From a viewpoint of “low-temperature characteristic”, the content of thephosphazene derivative of the formula (III) in the electrolyte ispreferably not less than 1% by volume, more preferably not less than 3%by volume, further preferably not less than 5% by volume, and the totalcontent of the isomer of the formula (VI) and the phosphazene derivativeof the formula (VII) is preferably not less than 1% by volume, morepreferably not less than 2% by volume, further preferably not less than5% by volume. When the content is less than 1% by volume, thelow-temperature characteristic of the electrolyte is not sufficient.

From a viewpoint of “deterioration resistance”, the content of thephosphazene derivative of the formula (III) in the electrolyte ispreferably not less than 2% by volume, more preferably not less than 3%by volume, and the content of the phosphazene derivative of the formula(IV) is preferably not less than 2% by volume, more preferably not lessthan 3% by volume, and the content of the phosphazene derivative of theformula (V) is preferably not less than 2% by volume, and the totalcontent of the isomer of the formula (VI) and the phosphazene derivativeof the formula (VII) is preferably not less than 2% by volume, morepreferably not less than 3% by volume. When the content is within theabove range, the deterioration of the electrolyte can be preferablysuppressed.

From a viewpoint of “lowering of viscosity”, the content of thephosphazene derivative of the formula (III) in the electrolyte ispreferably not less than 3% by volume when being included in anelectrolyte having a viscosity higher than that of this phosphazenederivative, and preferably 3-80% by volume, more preferably 3-50% byvolume when being included in an electrolyte having a viscosity lowerthan that of this phosphazene derivative.

From a viewpoint of “control of viscosity rise”, the content of thephosphazene derivative of the formula (V) in the electrolyte ispreferably not more than 40% by weight, more preferably not more than35% by weight, further preferably not more than 30% by weight. When thecontent exceeds 40% by weight, the viscosity rise of the electrolytebecomes remarkably large and the internal resistance is high and theelectric conductivity becomes undesirably low.

From viewpoints of “safety”, “self-extinguishing property” and “flameretardance”, a case of including the cyclic phosphazene derivative ofthe formula (IV) or (V), or the isomer of the formula (VI) and thephosphazene derivative of the formula (VII) and LiBF₄ or LiCF₃SO₃, andγ-butyrolactone and/or propylene carbonate is particularly preferable asthe electrolyte. In this case, even if the content is small, the safety,self-extinguishing property and flame retardance are very highirrespectively of the aforementioned description.

That is, the content of the cyclic phosphazene derivative of the formula(IV) in the electrolyte is preferably not less than 5% by volume inorder to particularly develop the excellent safety. Also, the content ofthe cyclic phosphazene derivative of the formula (V) in the electrolyteis preferably 5-10% by weight in case of including LiBF₄ in order todevelop the self-extinguishing property and preferably more than 10% byweight in order to develop the flame retardance, and preferably 5-25% byweight in case of including LiCF₃SO₃ in order to develop theself-extinguishing property and preferably more than 25% by weight inorder to develop the flame retardance. Furthermore, the total content ofthe isomer of the formula (VI) and the phosphazene derivative of theformula (VII) in the electrolyte is preferably 1.5-10% by volume in caseof including LiBF₄ in order to develop the self-extinguishing propertyand preferably more than 10% by volume in order to develop the flameretardance, and preferably 2.5-15% by volume in case of includingLiCF₃SO₃ in order to develop the self-extinguishing property andpreferably more than 15% by volume in order to develop the flameretardance. Moreover, if it is intended to use at a high temperature, acase of including Li(C₂F₅SO₂)₂N, Li(CF₃SO₂)₂N and LiBF₄ as a supportsalt is also preferable.

Other Members

As the other member used in the lithium primary cell of the invention ismentioned a separator interposing between the positive and negativeelectrodes in the lithium primary cell for preventing theshort-circuiting of current due to the contact of both electrodes. As amaterial of the separator is preferably mentioned a material capable ofsurely preventing the contact of both electrodes and passing orincluding the electrolyte such as non-woven fabric, thin-layer film orthe like made of a synthetic resin such as polytetrafluoroethylene,polypropylene, polyethylene, cellulose base, polybutylene terephthalate,polyethylene terephthalate or the like. Among them, a microporous filmof polypropylene or polyethylene having a thickness of about 20-50 μmand a film of cellulose base, polybutylene terephthalate, polyethyleneterephthalate or the like are particularly preferable.

In the invention, various known members usually used in the cell can bepreferably used in addition to the separator.

Form of Lithium Primary Cell

The form of the aforementioned lithium primary cell according to theinvention is not particularly limited, and preferably includes variousknown forms such as cylindrical cells of coin type, button type, papertype, rectangular or spiral structure and the like. In case of buttontype, a lithium primary cell can be prepared by providing sheet-shapedpositive electrode and negative electrode, and sandwiching a separatorbetween the positive and negative electrodes and the like. In case ofspiral structure, a lithium primary cell can be prepared by providingsheet-shaped positive electrodes, sandwiching a collector therebetween,piling a negative electrode (sheet-shaped) thereon and winding them andthe like.

The following examples are given in illustration of the invention andare not intended as limitations thereof.

EXAMPLE 1

A positive electrode for a lithium primary cell is prepared by thefollowing method. A paste is prepared by mixing and kneading 20 mg ofelectrochemically synthesized manganese dioxide made by Toso Co., Ltd.,0.1 mL of a phosphazene derivative A (a cyclic phosphazene derivativecompound of the formula (IV) in which n is 3 and two of six R⁵s areethoxy group and the remaining four are fluorine, viscosity at 25° C.:1.2 mPa·s (1.2 cP)), 12.5 mg of acetylene black and 1.2 mg ofpolyvinylidene fluoride in air for 30 minutes. Then, the paste isapplied through a doctor blade and dried with hot air (100-120° C.) andthen cut out by a punching machine of φ16 mm to prepare a positiveelectrode for the lithium primary cell.

By using such a positive electrode is prepared a lithium primary cell asfollows. Moreover, a lithium foil (thickness 0.5 mm) is punched out intoφ16 mm and used as a negative electrode, and a nickel foil is used as acollector. Also, an electrolyte is prepared by dissolving LiCF₃SO₃ at aconcentration of 0.75 mol/L (M) in a mixed solution of 50 volume % ofpropylene carbonate (PC) and 50 volume % of dimethoxyethane (DME). As aseparator is used a polyethylene separator made by Tonen-Sha, throughwhich the positive and negative electrodes are opposed and the aboveelectrolyte is poured therein and sealed to prepare a CR2016 typelithium primary cell.

After an initial cell voltage at 20° C. is measured and evaluated withrespect to the thus obtained cell, average discharge potential,discharge capacity at room temperature and energy density are measuredand evaluated by the following evaluation methods. These results areshown in Table 1.

Evaluation of Average Discharge Potential

The average discharge potential is measured as follows. In a dischargecurve obtained by discharging to the positive electrode material under acondition of 0.2C, a potential keeping a flatness is measured as anaverage discharge potential.

Evaluation of Discharge Capacity at Room Temperature

The discharge capacity is measured by conducting the discharge of 0.2Cat a lower limit voltage of 1.5 V under an environment of 20° C.

Evaluation of Energy Density

The energy density is determined by calculating a discharge capacity perunit weight from the above discharge capacity at room temperature.

Evaluation of Internal Resistance of Cell

The measurement of the internal resistance of the cell is carried out byusing a complex impedance measuring apparatus (impedance analyzer SI1260 and electrical interface SI 1287, made by Toyu Technica Co., Ltd.),measuring a resistance component (R) and a capacity component (C) ateach frequency (f) within a frequency range of 0.1-10⁶ Hz and plottingcomplex impedances when an abscissa is Z′(Ω) (=R) and an ordinate is Z″(=½πfC). Moreover, Z′(Ω) at f=1 kHz (real number term, hereinafterreferred to as 1 KHz Z′(Ω)) is frequently evaluated as an internalresistance of a cell itself, so that 1 kHz Z′(Ω) in the cells of theexamples and comparative examples are evaluated as the internalresistance of the cell itself.

EXAMPLE 2

A positive electrode is prepared in the same manner as in Example 1except that a phosphazene derivative B (a cyclic phosphazene derivativeof the formula (IV) in which n is 3 and one of six R⁵s is ethoxy groupand the remaining five are fluorine, viscosity at 25° C.: 1.2 mPa·s (1.2cP)) is used instead of the phosphazene derivative A, and then a lithiumprimary cell is prepared. With respect to the thus obtained lithiumprimary cell, the initial voltage, average discharge potential, 1 kHzZ′(Ω), discharge capacity and energy density are measured in the samemanner as in Example 1 to obtain results shown in Table 1.

EXAMPLE 3

A positive electrode is prepared in the same manner as in Example 1except that a phosphazene derivative C (a cyclic phosphazene derivativeof the formula (IV) in which n is 3 and one of six R⁵s is methoxy groupand the remaining five are fluorine, viscosity at 25° C.: 1.8 mPa·s (1.8cP)) is used instead of the phosphazene derivative A, and then a lithiumprimary cell is prepared. With respect to the thus obtained lithiumprimary cell, the initial voltage, average discharge potential, 1 kHzZ′(Ω), discharge capacity and energy density are measured in the samemanner as in Example 1 to obtain results shown in Table 1.

EXAMPLE 4

A positive electrode is prepared in the same manner as in Example 1except that a phosphazene derivative D (a cyclic phosphazene derivativeof the formula (IV) in which n is 3 and one of six R⁵s is n-propoxygroup and the remaining five are fluorine, viscosity at 25° C.: 1.1mPa·s (1.1 cP)) is used instead of the phosphazene derivative A, andthen a lithium primary cell is prepared. With respect to the thusobtained lithium primary cell, the initial voltage, average dischargepotential, 1 kHz Z′(Ω), discharge capacity and energy density aremeasured in the same manner as in Example 1 to obtain results shown inTable 1.

EXAMPLE 5

A positive electrode is prepared in the same manner as in Example 1except that a phosphazene derivative E (a cyclic phosphazene derivativeof the formula (IV) in which n is 3 and two of six R⁵s are OCH₂CF₃ andthe remaining four are fluorine, viscosity at 25° C.: 3.2 mPa·s (3.2cP)) is used instead of the phosphazene derivative A, and then a lithiumprimary cell is prepared. With respect to the thus obtained lithiumprimary cell, the initial voltage, average discharge potential, 1 kHzZ′(Ω), discharge capacity and energy density are measured in the samemanner as in Example 1 to obtain results shown in Table 1.

EXAMPLE 6

A positive electrode is prepared in the same manner as in Example 1except that a phosphazene derivative F (a chain phosphazene derivativeof the formula (I) in which Y¹-Y³ are O (oxygen), R¹-R³ are CH₂CF₃ andX¹ is P(O)(OCH₂CF₃)₂, viscosity at 25° C.: 18.9 mPa·s (18.9 cP)) is usedinstead of the phosphazene derivative A, and then a lithium primary cellis prepared. With respect to the thus obtained lithium primary cell, theinitial voltage, average discharge potential, 1 kHz Z′(Ω), dischargecapacity and energy density are measured in the same manner as inExample 1 to obtain results shown in Table 1.

EXAMPLE 7

A positive electrode is prepared in the same manner as in Example 1except that a phosphazene derivative G (a chain phosphazene derivativeof the formula (I) in which Y¹-Y³ are O (oxygen), R¹-R³ are CH₂CH₃ andX¹ is P(O)(OCH₂CH₃), viscosity at 25° C.: 5.8 mPa·s (5.8 cP)) is usedinstead of the phosphazene derivative A, and then a lithium primary cellis prepared. With respect to the thus obtained lithium primary cell, theinitial voltage, average discharge potential, 1 kHz Z′(Ω), dischargecapacity and energy density are measured in the same manner as inExample 1 to obtain results shown in Table 1.

CONVENTIONAL EXAMPLE 1

A positive electrode is prepared in the same manner as in Example 1except that the phosphazene derivative A is not used, and then a lithiumprimary cell is prepared. With respect to the thus obtained lithiumprimary cell, the initial voltage, average discharge potential, 1 kHzZ′(Ω), discharge capacity and energy density are measured in the samemanner as in Example 1 to obtain results shown in Table 1.

EXAMPLE 8

A positive electrode is prepared in the same manner as in Example 1except that graphite fluoride made by Daikin Co., Ltd. is used insteadof the electrochemically synthesized manganese dioxide made by Toso Co.,Ltd., and then a lithium primary cell is prepared. With respect to thethus obtained lithium primary cell, the initial voltage, averagedischarge potential, 1 kHz Z′(Ω), discharge capacity and energy densityare measured in the same manner as in Example 1 to obtain results shownin Table 1.

EXAMPLES 9-14

A positive electrode is prepared in the same manner as in Example 8except that each of phosphazenes shown in Table 1 is used instead of thephosphazene derivative A, and then a lithium primary cell is prepared.With respect to the thus obtained lithium primary cells, the initialvoltage, average discharge potential, 1 kHz Z′(Ω), discharge capacityand energy density are measured in the same manner as in Example 1 toobtain results shown in Table 1.

CONVENTIONAL EXAMPLE 2

A positive electrode is prepared in the same manner as in Example 8except that the phosphazene derivative A is not used, and then a lithiumprimary cell is prepared. With respect to the thus obtained lithiumprimary cell, the initial voltage, average discharge potential, 1 kHzZ′(Ω), discharge capacity and energy density are measured in the samemanner as in Example 1 to obtain results shown in Table 1. TABLE 1Positive electrode material Cell characteristics Active Averagesubstance Initial discharge Discharge Energy for positive Phosphazenevoltage potential 1 kHz Z′ capacity density electrode derivative (V) (V)(Ω) (mAh/g) (Wh/kg) Example 1 MnO₂ phosphazene A 3.47 2.90 35.5 290 772Example 2 MnO₂ phosphazene B 3.48 2.90 34.5 292 780 Example 3 MnO₂phosphazene C 3.47 2.90 35.0 290 770 Example 4 MnO₂ phosphazene D 3.472.90 34.0 294 788 Example 5 MnO₂ phosphazene E 3.48 2.90 35.2 290 772Example 6 MnO₂ phosphazene F 3.47 2.90 36.3 285 753 Example 7 MnO₂phosphazene G 3.47 2.90 36.4 285 752 Conventional MnO₂ none 3.45 2.8545.0 278 739 Example 1 Example 8 (CF_(x))_(n) phosphazene A 3.30 2.4285.0 230 590 Example 9 (CF_(x))_(n) phosphazene B 3.31 2.41 84.0 231 592Example 10 (CF_(x))_(n) phosphazene C 3.28 2.40 86.5 235 580 Example 11(CF_(x))_(n) phosphazene D 3.32 2.42 83.5 232 594 Example 12(CF_(x))_(n) phosphazene E 3.33 2.43 83.0 225 580 Example 13(CF_(x))_(n) phosphazene F 3.27 2.40 87.0 223 576 Example 14(CF_(x))_(n) phosphazene G 3.29 2.39 86.0 227 584 Conventional(CF_(x))_(n) none 3.10 2.30 150.0 210 550 Example 2

As seen from Table 1, the internal resistance of the cell itself islowered and the discharge capacity and energy density are improved bymixing and kneading the phosphazene derivative with the active substancefor positive electrode to prepare the positive electrode.

EXAMPLE 15

A positive electrode is prepared in the same manner as in Example 1.Also, an electrolyte is prepared by dissolving LiCF₃SO₃ (lithium salt)at a concentration of 0.75 mol/L (M) in a mixed solution of 10 volume %of the phosphazene derivative A (a cyclic phosphazene derivativecompound of the formula (IV) in which n is 3 and two of six R⁵s areethoxy group and the remaining four are fluorine, viscosity at 25° C.:1.2 mPa·s (1.2 cP)), 45 volume % of propylene carbonate (PC) and 45volume % of dimethoxyethane (DME). A lithium primary cell is prepared inthe same manner as in Example 1 by using the positive electrode andelectrolyte. With respect to the thus obtained lithium primary cell, theinitial voltage, average discharge potential, 1 kHz Z′(Ω), dischargecapacity and energy density are measured in the same manner as inExample 1. Also, the limit oxygen index of the electrolyte is measuredaccording to JIS K7201. The results are shown in Table 2.

EXAMPLE 16

A positive electrode is prepared in the same manner as in Example 1.Also, an electrolyte is prepared by dissolving LiCF₃SO₃ (lithium salt)at a concentration of 0.75 mol/L (M) in a mixed solution of 10 volume %of the phosphazene derivative D (a cyclic phosphazene derivativecompound of the formula (IV) in which n is 3 and one of six R⁵s isn-propoxy group and the remaining five are fluorine, viscosity at 25°C.: 1.1 mPa·s (1.1 cP)), 45 volume % of propylene carbonate (PC) and 45volume % of dimethoxyethane (DME). A lithium primary cell is prepared inthe same manner as in Example 1 by using the positive electrode andelectrolyte. With respect to the thus obtained lithium primary cell, theinitial voltage, average discharge potential, 1 kHz Z′(Ω), dischargecapacity and energy density are measured in the same manner as inExample 1. Also, the limit oxygen index of the electrolyte is measuredin the same manner as in Example 15. The results are shown in Table 2.

EXAMPLE 17

A positive electrode is prepared in the same manner as in Example 1except that a phosphazene derivative E (a cyclic phosphazene derivativeof the formula (IV) in which n is 3 and two of six R⁵s are OCH₂CF₃ andthe remaining four are fluorine, viscosity at 25° C.: 3.2 mPa·s (3.2cP)) is used instead of the phosphazene derivative A. Also, anelectrolyte is prepared by dissolving LiBF4 (lithium salt) at aconcentration of 0.75 mol/L (M) in a mixed solution of 10 volume % ofthe phosphazene derivative E and 90 volume % of γ-butyrolactone (GBL). Alithium primary cell is prepared in the same manner as in Example 1 byusing the positive electrode and electrolyte. With respect to the thusobtained lithium primary cell, the initial voltage, average dischargepotential, 1 kHz Z′(Ω), discharge capacity and energy density aremeasured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

EXAMPLE 18

A lithium primary cell is prepared in the same manner as in Example 17except that Li(C₂F₅SO₂)₂N is used instead of LiBF₄. With respect to thethus obtained lithium primary cell, the initial voltage, averagedischarge potential, 1 kHz Z′(Ω), discharge capacity and energy densityare measured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

EXAMPLE 19

A positive electrode is prepared in the same manner as in Example 17.Also, an electrolyte is prepared in the same manner as in Example 17except that the phosphazene derivative H (a cyclic phosphazenederivative compound of the formula (IV) in which n is 3 and two of sixR⁵s are n-propoxy group and the remaining four are fluorine, viscosityat 25° C.: 1.2 mPa·s (1.2 cP)) is used instead of the phosphazenederivative E. A lithium primary cell is prepared in the same manner asin Example 1 by using the positive electrode and electrolyte. Withrespect to the thus obtained lithium primary cell, the initial voltage,average discharge potential, 1 kHz Z′(Ω), discharge capacity and energydensity are measured in the same manner as in Example 1. Also, the limitoxygen index of the electrolyte is measured in the same manner as inExample 15. The results are shown in Table 2.

EXAMPLE 20

A positive electrode is prepared in the same manner as in Example 17.Also, an electrolyte is prepared in the same manner as in Example 17except that the phosphazene derivative F (a chain phosphazene derivativecompound of the formula (I) in which Y¹-Y³ are O (oxygen), R¹-R³ areCH₂CF₃ and X¹ is P(O)(OCH₂CF₃)₂, viscosity at 25° C.: 18.9 mPa·s (18.9cP)) is used instead of the phosphazene derivative E. A lithium primarycell is prepared in the same manner as in Example 1 by using thepositive electrode and electrolyte. With respect to the thus obtainedlithium primary cell, the initial voltage, average discharge potential,1 kHz Z′(Ω), discharge capacity and energy density are measured in thesame manner as in Example 1. Also, the limit oxygen index of theelectrolyte is measured in the same manner as in Example 15. The resultsare shown in Table 2.

EXAMPLE 21

A positive electrode is prepared in the same manner as in Example 1except that the phosphazene derivative F is used instead of thephosphazene derivative A. Also, an electrolyte is prepared in the samemanner as in Example 20. A lithium primary cell is prepared in the samemanner as in Example 1 by using the positive electrode and electrolyte.With respect to the thus obtained lithium primary cell, the initialvoltage, average discharge potential, 1 kHz Z′(Ω), discharge capacityand energy density are measured in the same manner as in Example 1.Also, the limit oxygen index of the electrolyte is measured in the samemanner as in Example 15. The results are shown in Table 2.

EXAMPLE 22

A positive electrode is prepared in the same manner as in Example 17.Also, an electrolyte is prepared in the same manner as in Example 17except that the phosphazene derivative G (a chain phosphazene derivativecompound of the formula (I) in which Y¹-Y³ are O (oxygen), R¹-R³ areCH₂CH₃ and X¹ is P(O)(OCH₂CH₃)₂, viscosity at 25° C.: 5.8 mPa·s (5.8cP)) is used instead of the phosphazene derivative E. A lithium primarycell is prepared in the same manner as in Example 1 by using thepositive electrode and electrolyte. With respect to the thus obtainedlithium primary cell, the initial voltage, average discharge potential,1 kHz Z′(Ω), discharge capacity and energy density are measured in thesame manner as in Example 1. Also, the limit oxygen index of theelectrolyte is measured in the same manner as in Example 15. The resultsare shown in Table 2.

EXAMPLE 23

A positive electrode is prepared in the same manner as in Example 17.Also, an electrolyte is prepared by dissolving LiBF₄ (lithium salt) at aconcentration of 0.75 mol/L (M) in a mixed solution of 10 volume % ofthe phosphazene derivative E and 90 volume % of propylene carbonate(PC). A lithium primary cell is prepared in the same manner as inExample 1 by using the positive electrode and electrolyte. With respectto the thus obtained lithium primary cell, the initial voltage, averagedischarge potential, 1 kHz Z′(Ω), discharge capacity and energy densityare measured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

EXAMPLE 24

A positive electrode is prepared in the same manner as in Example 17.Also, an electrolyte is prepared in the same manner as in Example 23except that the phosphazene derivative H is used instead of thephosphazene derivative E. A lithium primary cell is prepared in the samemanner as in Example 1 by using the positive electrode and electrolyte.With respect to the thus obtained lithium primary cell, the initialvoltage, average discharge potential, 1 kHz Z′(Ω), discharge capacityand energy density are measured in the same manner as in Example 1.Also, the limit oxygen index of the electrolyte is measured in the samemanner as in Example 15. The results are shown in Table 2.

CONVENTIONAL EXAMPLE 1

The limit oxygen index of the electrolyte used in the above ConventionalExample 1 is measured in the same manner as in Example 15. The result isshown in Table 2.

CONVENTIONAL EXAMPLE 3

A positive electrode is prepared in the same manner as in ConventionalExample 1. Also, an electrolyte is prepared in the same manner as inExample 15. A lithium primary cell is prepared in the same manner as inExample 1 by using the positive electrode and electrolyte. With respectto the thus obtained lithium primary cell, the initial voltage, averagedischarge potential, 1 kHz Z′(Ω), discharge capacity and energy densityare measured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

CONVENTIONAL EXAMPLE 4

A positive electrode is prepared in the same manner as in ConventionalExample 1. Also, an electrolyte is prepared in the same manner as inExample 17 except that the phosphazene derivative E is not added. Alithium primary cell is prepared in the same manner as in Example 1 byusing the positive electrode and electrolyte. With respect to the thusobtained lithium primary cell, the initial voltage, average dischargepotential, 1 kHz Z′(Ω), discharge capacity and energy density aremeasured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

CONVENTIONAL EXAMPLE 5

A positive electrode is prepared in the same manner as in ConventionalExample 1. Also, an electrolyte is prepared in the same manner as inExample 17. A lithium primary cell is prepared in the same manner as inExample 1 by using the positive electrode and electrolyte. With respectto the thus obtained lithium primary cell, the initial voltage, averagedischarge potential, 1 kHz Z′(Ω), discharge capacity and energy densityare measured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

CONVENTIONAL EXAMPLE 6

A positive electrode is prepared in the same manner as in ConventionalExample 1. Also, an electrolyte is prepared in the same manner as inExample 23 except that the phosphazene derivative E is not added. Alithium primary cell is prepared in the same manner as in Example 1 byusing the positive electrode and electrolyte. With respect to the thusobtained lithium primary cell, the initial voltage, average dischargepotential, 1 kHz Z′(Ω), discharge capacity and energy density aremeasured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

CONVENTIONAL EXAMPLE 7

A positive electrode is prepared in the same manner as in ConventionalExample 1. Also, an electrolyte is prepared in the same manner as inExample 23. A lithium primary cell is prepared in the same manner as inExample 1 by using the positive electrode and electrolyte. With respectto the thus obtained lithium primary cell, the initial voltage, averagedischarge potential, 1 kHz Z′(Ω), discharge capacity and energy densityare measured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

EXAMPLE 25

A positive electrode is prepared in the same manner as in Example 1except that graphite fluoride made by Daikin Co., Ltd. is used insteadof the electrochemically synthesized manganese dioxide made by Toso Co.,Ltd. and the phosphazene derivative E is used instead of the phosphazenederivative A. Also, an electrolyte is prepared in the same manner as inExample 17 except that the phosphazene derivative D is used instead ofthe phosphazene derivative E. A lithium primary cell is prepared in thesame manner as in Example 1 by using the positive electrode andelectrolyte. With respect to the thus obtained lithium primary cell, theinitial voltage, average discharge potential, 1 kHz Z′(Ω), dischargecapacity and energy density are measured in the same manner as inExample 1. Also, the limit oxygen index of the electrolyte is measuredin the same manner as in Example 15. The results are shown in Table 2.

EXAMPLE 26

A positive electrode is prepared in the same manner as in Example 25.Also, an electrolyte is prepared in the same manner as in Example 17. Alithium primary cell is prepared in the same manner as in Example 1 byusing the positive electrode and electrolyte. With respect to the thusobtained lithium primary cell, the initial voltage, average dischargepotential, 1 kHz Z′(Ω), discharge capacity and energy density aremeasured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2.

CONVENTIONAL EXAMPLE 2

The limit oxygen index of the electrolyte used in the above ConventionalExample 2 is measured in the same manner as in Example 15. The result isshown in Table 2.

CONVENTIONAL EXAMPLE 8

A positive electrode is prepared in the same manner as in ConventionalExample 2. Also, an electrolyte is prepared in the same manner as inExample 25. A lithium primary cell is prepared in the same manner as inExample 1 by using the positive electrode and electrolyte. With respectto the thus obtained lithium primary cell, the initial voltage, averagedischarge potential, 1 kHz Z′(Ω), discharge capacity and energy densityare measured in the same manner as in Example 1. Also, the limit oxygenindex of the electrolyte is measured in the same manner as in Example15. The results are shown in Table 2. TABLE 2 Positive electrodematerial Electrolyte Cell characteristics Active Limit Initial Average 1substance Aprotic oxygen volt- discharge kHz Discharge Energy forpositive Phosphazene organic Phosphazene index age potential Z′ capacitydensity electrode derivative solvent derivative Support salt (vol %) (V)(V) (Ω) (mAh/g) (Wh/kg) Example 15 MnO₂ phosphazene A PC/DME =phosphazene A LiCF₃SO₃ 22.0 3.47 2.90 32.2 295.0 790.0 1/1 Example 16MnO₂ phosphazene A PC/DME = phosphazene D LiCF₃SO₃ 25.0 3.47 2.90 32.2295.0 790.0 1/1 Example 17 MnO₂ phosphazene E GBL phosphazene E LiBF₄22.4 3.47 2.90 30.0 298.0 815.0 Example 18 MnO₂ phosphazene E GBLphosphazene E Li(C₂F₅SO₂)₂N 21.9 3.47 2.90 32.1 295.0 790.0 Example 19MnO₂ phosphazene E GBL phosphazene H LiBF₄ 23.8 3.47 2.90 32.1 295.0790.0 Example 20 MnO₂ phosphazene E GBL phosphazene F LiBF₄ 21.6 3.472.90 32.1 295.0 790.0 Example 21 MnO₂ phosphazene F GBL phosphazene FLiBF₄ 21.6 3.47 2.90 32.1 295.0 790.0 Example 22 MnO₂ phosphazene F GBLphosphazene G LiBF₄ 21.1 3.47 2.90 33.0 294.0 772.0 Example 23 MnO₂phosphazene E PC phosphazene E LiBF₄ 22.4 3.47 2.90 34.0 293.0 780.0Example 24 MnO₂ phosphazene E PC phosphazene H LiBF₄ 23.8 3.47 2.90 37.0291.0 770.0 Conventional MnO₂ — PC/DME = — LiCF₃SO₃ 15.4 3.45 2.85 45.0278.0 739.0 Example 1 1/1 Conventional MnO₂ — PC/DME = phosphazene ALiCF₃SO₃ 22.0 3.47 2.90 35.5 290.0 772.0 Example 3 1/1 Conventional MnO₂— GBL — LiBF₄ 18.0 3.45 2.85 43.0 279.0 744.0 Example 4 ConventionalMnO₂ — GBL phosphazene E LiBF₄ 22.4 3.47 2.90 37.0 291.0 770.0 Example 5Conventional MnO₂ — PC — LiBF₄ 19.0 3.45 2.85 49.0 275.0 735.0 Example 6Conventional MnO₂ — PC phosphazene E LiBF₄ 22.4 3.47 2.90 40.0 285.0752.0 Example 7 Example 25 (CF_(x))_(n) phosphazene E GBL phosphazene DLiBF₄ 25.0 3.15 2.32 90.0 228.0 586.0 Example 26 (CF_(x))_(n)phosphazene E GBL phosphazene E LiBF₄ 22.4 3.15 2.32 95.0 226.0 582.0Conventional (CF_(x))_(n) — GBL — LiBF₄ 18.0 3.10 2.30 150.0 210.0 550.0Example 2 Conventional (CF_(x))_(n) — GBL phosphazene D LiBF₄ 25.0 3.122.32 100.0 225.0 580.0 Example 8

As seen from Table 2, by using the positive electrode made of the pastebody containing the active substance for positive electrode and thephosphazene derivative and using the electrolyte added with thephosphazene derivative, the internal resistance of the cell itself isfurther lowered, and the discharge capacity and energy density arefurther improved, and the limit oxygen index of the electrolyte israised to largely improve the safety.

INDUSTRIAL APPLICABILITY

According to the invention, there can be provided a positive electrodemade of a paste body containing an active substance for positiveelectrode and a phosphazene derivative and/or an isomer of a phosphazenederivative, and a lithium primary cell having high discharge capacityand energy density and a high output and a long service life can beprovided by using such a positive electrode.

Also, when the lithium primary cell is constructed by using a positiveelectrode made of a paste body containing an active substance forpositive electrode and a phosphazene derivative and/or an isomer of aphosphazene derivative and an electrolyte added with a phosphazenederivative and/or an isomer of a phosphazene derivative, there can beprovided a lithium primary cell having high discharge capacity andenergy density and a high output and a long service life and a highsafety.

1. A positive electrode for a lithium primary cell comprising a pastebody containing an active substance for positive electrode and aphosphazene derivative and/or an isomer of a phosphazene derivative. 2.A positive electrode for a lithium primary cell according to claim 1,wherein a total mass of the phosphazene derivative and/or the isomer ofthe phosphazene derivative is a mass corresponding to 0.01 to 100 timesa mass of the active substance for positive electrode.
 3. A positiveelectrode for a lithium primary cell according to claim 1 or 2, whereinthe phosphazene derivative has a viscosity at 25° C. of not more than100 mPa·s (100 cP) and is represented by the following formula (I) or(II):

(wherein R¹, R² and R³ are independently a monovalent substituent or ahalogen element; X¹ is a substituent containing at least one elementselected from the group consisting of carbon, silicon, germanium, tin,nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur,selenium, tellurium and polonium; and Y¹, Y² and Y³ are independently abivalent connecting group, a bivalent element or a single bond)(NPR⁴ ₂)_(n)  (II) (wherein R⁴ is independently a monovalent substituentor a halogen element; and n is 3 to 15).
 4. A positive electrode for alithium primary cell according to claim 3, wherein the phosphazenederivative of the formula (II) is represented by the following formula(III):(NPF₂)_(n)  (III) (wherein n is 3 to 15).
 5. A positive electrode for alithium primary cell according to claim 3, wherein the phosphazenederivative of the formula (II) is represented by the following formula(IV):(NPR⁵ ₂)_(n)  (IV) (wherein R⁵ is independently a monovalent substituentor a halogen element and at least one of all R⁵s is afluorine-containing monovalent substituent or fluorine, and n is 3 to15, provided that all R⁵s are not fluorine).
 6. A positive electrode fora lithium primary cell according to claim 1 or 2, wherein thephosphazene derivative is a solid at 25° C. and is represented by thefollowing formula (V):(NPR⁶ ₂)_(n)  (V) (wherein R⁶ is independently a monovalent substituentor a halogen element; and n is 3 to 15).
 7. A positive electrode for alithium primary cell according to claim 1 or 2, wherein the isomer isrepresented by the following formula (VI) and is an isomer of aphosphazene derivative represented by the following formula (VII):

(in the formulae (VI) and (VII), R⁷, R⁸ and R⁹ are independently amonovalent substituent or a halogen element; X is a substituentcontaining at least one element selected from the group consisting ofcarbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic,antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium; andY⁷ and Y⁸ are independently a bivalent connecting group, a bivalentelement or a single bond).
 8. A method of producing a positive electrodefor a lithium primary cell, characterized by comprising (I) a step ofmilling an active substance for positive electrode and a phosphazenederivative and/or an isomer of a phosphazene derivative to produce apaste; and (II) a step of applying the paste to a positive electrodemanufacturing jig and drying and shaping into a desired form to producea positive electrode of a paste body.
 9. A lithium primary electrodecomprising a positive electrode described in claim 1, a negativeelectrode, and an electrolyte comprising an aprotic organic solvent anda support salt.
 10. A lithium primary cell according to claim 9, whereinthe aprotic organic solvent is added with a phosphazene derivativeand/or an isomer of a phosphazene derivative.
 11. A lithium primary cellaccording to claim 10, wherein the phosphazene derivative and/or theisomer of the phosphazene derivative included in the positive electrodeare the same as the phosphazene derivative and/or the isomer of thephosphazene derivative added to the aprotic organic solvent.
 12. Alithium primary cell according to claim 10, wherein the phosphazenederivative and/or the isomer of the phosphazene derivative included inthe positive electrode are different from the phosphazene derivativeand/or the isomer of the phosphazene derivative added to the aproticorganic solvent.
 13. A lithium primary cell according to any one ofclaims 10 to 12, wherein the phosphazene derivative added to the aproticorganic solvent has a viscosity at 25° C. of not more than 100 mPa·s(100 cP) and is represented by the following formula (I) or (II):

(wherein R¹, R² and R³ are independently a monovalent substituent or ahalogen element; X¹ is a substituent containing at least one elementselected from the group consisting of carbon, silicon, germanium, tin,nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur,selenium, tellurium and polonium; and Y¹, Y² and Y³ are independently abivalent connecting group, a bivalent element or a single bond)(NPR⁴ ₂)_(n)  (II) (wherein R⁴ is independently a monovalent substituentor a halogen element; and n is 3 to 15).
 14. A lithium primary cellaccording to claim 13, wherein the phosphazene derivative of the formula(II) is represented by the following formula (III):(NPF₂)_(n)  (III) (wherein n is 3 to 15).
 15. A lithium primary cellaccording to claim 13, wherein the phosphazene derivative of the formula(II) is represented by the following formula (IV):(NPR⁵ ₂)_(n)  (IV) (wherein R⁵ is independently a monovalent substituentor a halogen element and at least one of all R⁵s is afluorine-containing monovalent substituent or fluorine, and n is 3 to15, provided that all R⁵s are not fluorine).
 16. A lithium primary cellaccording to any one of claims 10 to 12, wherein the phosphazenederivative added to the aprotic organic solvent is a solid at 25° C. andis represented by the following formula (V):(NPR⁶ ₂)_(n)  (V) (wherein R⁶ is independently a monovalent substituentor a halogen element; and n is 3 to 15).
 17. A lithium primary cellaccording to any one of claims 10 to 12, wherein the isomer of thephosphazene derivative added to the aprotic organic solvent isrepresented by the following formula (VI) and is an isomer of aphosphazene derivative represented by the following formula (VII):

(in the formulae (VI) and (VII), R⁷, R⁸ and R⁹ are independently amonovalent substituent or a halogen element; X² is a substituentcontaining at least one element selected from the group consisting ofcarbon, silicon, germanium, tin, nitrogen, phosphorus, arsenic,antimony, bismuth, oxygen, sulfur, selenium, tellurium and polonium; andY⁷ and Y⁸ are independently a bivalent connecting group, a bivalentelement or a single bond).